She is very hard to fight, as much as how hard she gets you
However, if you show her the Temmflakes during the fight, and previously stack on water cups and get the carrot from the nerdy ghost girl you can do it, as long as you survive the special attack phase. That part was always too hard for me cuz of the implications and the voice lines distracting me. After that you can remove poison instead of attacking if you need to
You can use items and attack in the same turn, and if you fail too many times you can accept Chara's help as the "Chara's promise" that decreases damage taken up to 90% (which is handy)